Pyrrole, reaction with phenylhydrazone

Treatment of a mixture of acetophenone phenylhydrazone and dimethyl acetylenedi-carboxylate with aluminium chloride gives the ene hydrazone 98, which undergoes a spontaneous Fischer indole reaction to yield the pyrrole 99 with elimination of aniline (equation 41)62. 

Tetramethylpyrrole reacts with only the most electrophilic of the aryldiazonium cations ca. 103 times more slowly than pyrroles possessing a vacant ring site. The reaction can follow one of two routes. Displacement of a methyl group yields the 2-arylazopyrrole with the concomitant formation of methanol (54LA(589)196). Alternatively, the arylhydrazone of 2-formyl-3,4,5-trimethylpyrrole is formed (78JCR(S)339). A similar reaction of 2,3-dimethylindole with the phenyldiazonium cation yields the phenylhydrazone of 2-formyl-3-methylindole (73JA3400). 

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